Objective: The role of metabolic syndrome (MS) and its individual components in postmenopausal breast cancer (PBC) risk is still unclear. We reviewed and summarized epidemiological studies assessing the association of MS with the risk of PBC. Methods: We conducted an electronic search, without restrictions, for articles published before October 31, 2012. Every included study was to report risk estimates with 95% CIs for the association between MS and PBC. Study-specific estimates were pooled using random-effects models. Results: Nine articles (with 6,417 cancer cases), all published in English, were included in the meta-analysis. MS was associated with a 52% increase in cancer risk (P < 0.001)-for the most part confined to noncohort studies (109% increased risk); the risk estimates changed little, depending on populations (United States and Europe) and definition of the syndrome (traditional vs nontraditional). The risk estimates for PBC were 1.12 (P = 0.068) for higher values of body mass index/waist circumference, 1.19 (P = 0.005) for hyperglycemia (higher fasting glucose or diabetes), 1.13 (P = 0.027) for higher blood pressure, 1.08 (P = 0.248) for higher triglycerides, and 1.39 (P = 0.008) for lower high-density lipoprotein cholesterol. All these estimates were lower than those associated with MS in the same studies. Conclusions: MS is associated with a moderately increased risk of PBC. No single component explains the risk conveyed by the full syndrome.

Objective: The role of metabolic syndrome (MS) and its individual components in postmenopausal breast cancer (PBC) risk is still unclear. We reviewed and summarized epidemiological studies assessing the association of MS with the risk of PBC. Methods: We conducted an electronic search, without restrictions, for articles published before October 31, 2012. Every included study was to report risk estimates with 95% CIs for the association between MS and PBC. Study-specific estimates were pooled using random-effects models. Results: Nine articles (with 6,417 cancer cases), all published in English, were included in the meta-analysis. MS was associated with a 52% increase in cancer risk (P < 0.001)-for the most part confined to noncohort studies (109% increased risk); the risk estimates changed little, depending on populations (United States and Europe) and definition of the syndrome (traditional vs nontraditional). The risk estimates for PBC were 1.12 (P = 0.068) for higher values of body mass index/waist circumference, 1.19 (P = 0.005) for hyperglycemia (higher fasting glucose or diabetes), 1.13 (P = 0.027) for higher blood pressure, 1.08 (P = 0.248) for higher triglycerides, and 1.39 (P = 0.008) for lower high-density lipoprotein cholesterol. All these estimates were lower than those associated with MS in the same studies. Conclusions: MS is associated with a moderately increased risk of PBC. No single component explains the risk conveyed by the full syndrome.